1. Field
The present disclosure relates generally to aircraft parts and, in particular, to aircraft stringers. Still more particularly, the present disclosure relates to a method and apparatus for a composite stringer.
2. Background
Aircraft generally include an airframe, which may be regarded as an underlying skeleton to which skin panels are attached to form a smooth aerodynamic outer surface. The wings also include an underlying structure covered with skin panels. Typically, skin panels are light and thin to minimize the weight of the aircraft and increase its payload and range. Since skin panels are thin, they are generally flexible and require stiffening to prevent undesired movement, flexing, and vibration during flight.
Hat stringers have been used for decades in the aerospace industry for stiffening metal fuselage sections and metal wing skins on both commercial and military aircraft. These stringers are composed of thin metal panels with acute angles that result in a trapezoidal shape, rectangular shape, semi-circular shape, or some other suitable shape. Relatively simple metal-forming techniques are used to bend the metal into the acute angles required for this shape. These metal-forming techniques include brake forming or rolling the metal into the hat stringer shape. These techniques allow the production of hat stringers with tight, constant angular bends and straight or flat legs.
In manufacturing composite hat stringers, a hat stringer may be placed on a fuselage skin in which the interior of the hat stringer has a hollow section that is formed with a bladder. These bladders are inserted into the composite stringer prior to performing curing processes. A curing process is a process that toughens or hardens a polymer material in the composite stringer. These bladders are inflated to support the internal structure of the composite stringer during the curing process in an oven or autoclave.
One drawback with the use of bladders is that, in some cases, a bladder may deflate inside of a composite stringer during the curing process. This deflation may result in an improperly formed composite stringer that may not work properly. As a result, the composite stringer is discarded and a new stringer is manufactured. The problems that may occur with deflation of a bladder during curing of a composite stringer include, for example, an improper shape for the stringer, ply movement, ply wrinkling, or porosity.
Therefore, it would be advantageous to have a method and apparatus that overcomes the above-described problems.